Viola odorata L., Sweet Violet

Account Summary

Growth form and preferred habitats

V. odorata is a patch-forming, perennial with long, creeping stolons and flowers usually (but not always) sweetly perfumed. It grows in a range of habitats from damp, shady banks under trees, or in plantations, to more open conditions in hedgerows, scrub margins, on roadside banks and along laneways, usually near habitation from which it often arises as a garden escape. It very rarely occurs in so-called, native woodland. Sweet Violet is generally considered to favour fertile, base-rich, calcareous, alkaline to neutral, moist soils, but it seems to have quite wide tolerances of both soil conditions and levels of light and shade (Porter & Foley 2017).

V. odorata is the only scented violet species in the British Isles − all the other violets in these islands are of the so-called 'Dog-' or 'Horse-' variety, ie less highly regarded, wild, scentless types (Genders 1971; Grigson 1987).

Variation

Six named varieties based on leaf size and flower colour are listed by Porter & Foley (2017) and Sell & Murrell (2018).

Flowering reproduction

V. odorata is the earliest of the Viola species in B & I to come into flower, flowers often appearing as early as February. The flowers range in colour, but usually are dark violet, or white, or something in between. The spur is stout, pale lilac, violet or purplish-green, sometimes hooked upwards and it is not notched. Flowering can continue into late April and sometimes there is another flush of flowers in the autumn. The sweet fragrance attracts bees which collect nectar from the spur and pick up pollen as they do so (Proctor & Yeo 1973). The fruit capsule is rounded or slightly three-sided and is densely covered with short, patent (ie erect), hairs.

The flowers of V. odorata are homogamous and compatible with their own pollen. However, self-pollination and self-fertilisation is prevented by the irregular, two-lipped, zygomorphic structure of the flower. Nevertheless, in late spring and summer Sweet Violet produces small flowers that never open, the styles and stamens of which remain short and poorly developed. These flowers self-pollinate within the unopened bud, ie they are cleistogamous, and they set additional seed.

Seed dispersal

The globular capsule lies on the ground and splits open, but does not explode to release its seeds. Rather, the valves of the split capsule dry and shrink, spilling out the seeds under or near the parent plant.

V. odorata seeds bear a conspicuous 'elaiosome' or nutrient oil body that attracts ants (Ridley 1930). Studies show that seed carried to ant nests has a greater probability of seedling emergence than seeds placed randomly on or slightly below the soil surface. The advantage of ant dispersal is the relocation of the seed to a 'safe site', ie one with favourable soil moisture and nutrient conditions, enabling better seedling establishment than otherwise. Micro-environment conditions at the scale of the seed can vary dramatically over distances as small as 10 cm. Movement by ants reduces predation by butterfly larvae, small mammals and birds, all of which are distance-related, rather than density-dependent, mortality factors (Beattie & Lyons 1975; Culver & Beattie 1978, 1980; Howe & Smallwood 1982).

Fermanagh occurrence

In Fermanagh, V. odorata has been recorded in a total of 16 tetrads (3% of those in the VC), scattered throughout the lowlands, usually near habitation. The largest and most established stand in Fermanagh is at Old Crom Castle, where Sweet Violet covers a considerable area under lime trees. Nine of the stations in the VC are pre-1955 and only at Crom does the species appear long persistent, having survived there for at least 50 years.

British status and occurrence

The native range of V. odorata in B & I is clouded by a very long history of introduction and cultivation. Both Genders (1971) and Grigson (1987) state that in ancient times it was in commercial cultivation for the sweetening properties of its perfume, and by the Middle Ages it was in use for culinary, medicinal, cosmetic and perfumery purposes (Grieve 1931).

Irish status and occurrence

In Ireland, it is traditionally regarded as possibly native in some areas of the south – but perhaps also in the Midlands, as suggested in the BSBI Atlas (Perring & Walters 1976). This position is not followed in the New Atlas, where the supposed native Irish occurrence is more confined to the SE quarter of the island (Preston et al. 2002). There may also be something of a decline within the Irish native area, since many of the records are pre-1970 (28% of them by RSF's calculation). In the N & W of Ireland, V. odorata has long been acknowledged as a garden escape (Cybele Hibernica 1866; An Irish Flora 1996). The Irish Census Catalogue, with its, "not always native" contribution, is uncommitted on the matter (Scannell & Synnott 1987).

With its creeping habit, colonising ability and sometimes long persistence, V. odorata might best be considered in Ireland, "doubtfully native, but thoroughly established" (Bunker 1950). The Cat Alien Pl Ir (Reynolds 2002, p. 323) simply reports that V. odorata is, "considered an introduction or garden escape in many places".

Cultivation, uses and status of Viola odorata: The status of any Viola species is always likely to be decided on circumstantial evidence since the flowers produce little pollen and thus are very unlikely to appear in the fossil record (Godwin 1975; Webb 1985). The status question is made even more ambiguous when, as in the case of V. odorata, there is a very long history of cultivation and human use. Although it is sensible to be wary when identifying ancient plant references with modern species (Raven 2000), it seems probable that V. odorata was a plant known and referred to by the ancient Greek pastoral poet Theocritus (c 300-c 260 BC) (Lindsell 1937). Both Genders (1971) and Grigson (1987) state that in ancient times V. odorata was in commercial cultivation for the sweetening properties of its perfume.

By the Middle Ages, Sweet Violet was in use for culinary, medicinal, cosmetic and perfumery purposes (Grieve 1931), and it was held in great affection by both Gerard (1597) and Shakespeare, who made as many as 20 references to it in his plays and poems (Ryden 1977). Medicinal uses of the plant were many (Grieve 1931), most significant perhaps being as a laxative mild enough for use with infants. The species also has a historical use as a bronchial and cough remedy. Like its relative, Viola tricolor (Wild Pansy), it was also used to treat mild skin conditions. The fresh leaves of V. odorata have been used to relieve the pain of cancer, especially in the oesophagus where other pain relievers have failed. A syrup made of the flowers has been used to treat eye inflammation, sleeplessness, jaundice, coughs, bronchial ailments and throat pain (Grieve 1931; Vickery 1995).

European and world occurrence

It is clear from the above that the native range of V. odorata is clouded by its long history of cultivation and introduction, yet Hultén & Fries (1986) remark that it, "originates mainly from S and W Europe". The latter authors indicate that they can only tentatively delineate its original distribution − using a dotted line on their map to mark the supposed northern limit of the native range of the species (Hultén & Fries 1986, Map 1318). Their map shows the species as being native in England and Wales, S of a line between Hull and Liverpool, plus France and all territory S of the Alps, including the Balkan peninsula and eastwards to the shores of the Caspian Sea. Isolated stations are also shown around the E and S shores of the Mediterranean in Asia Minor and N Africa. There is some dispute as to the status of V. odorata in Denmark and S Sweden, but it is definitely regarded as a naturalised introduction in N & C Europe, Japan, N & S America, the Philippines and New Zealand (Hultén & Fries 1986, p. 1092).

Names

The name 'Viola' is the Latin name used for various sweet-scented flowers including stocks and wallflowers, and is derived from the Greek 'ion', which in an earlier form had an initial letter corresponding to 'v' or 'w', the digamma, which was later lost (Stearn 1992). Even without being a linguist, it is clear that the identification of ancient flowers by translation alone is an extremely risky undertaking. The Latin specific epithet 'odorata' means 'sweet-smelling' or 'fragrant' (Gilbert-Carter 1964). The English common name 'Violet' is of 14th century origin, derived from the Old French 'violette', a diminutive of 'viole', from the Latin name 'Viola', which as already mentioned, appears to have originally been given to Matthiola incana, now called Hoary Stock − the parent species of the garden Stocks, which have an aromatic spicy perfume − as well as to Viola odorata, Sweet Violet (Genders 1971; Grigson 1974).

Threats

None.

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